The effect of topdressing ratio of nitrogen, phosphorus and potassium on the growth rate, yield, biomass cumulative and distribution trait of salt-stressed cotton under film mulched drip irrigation was discussed and the topdressing ratio was optimized by the field experiment in south Xinjiang Autonomous Region. Seven treatments with different topdressing ratios of nitrogen, phosphorus and potassium (N∶P2O5∶K2O) were set in the field experiment, namely, CK(0∶0∶0), A(1∶1∶1), B(1∶0.25∶1.25), C(1∶0.4∶0.27), D(1∶0.23∶0.20), E(1∶0.34∶0.23) and F(1∶0.17∶0). The accumulation and distribution of dry matter, yield and harvest index of cotton were measured accordingly. The results showed that compared with the average colony growth rate of CK, treatments of C, E, A, B, D and F increased by 19.56%, 18.17%, 15.65%, 13.50%, 10.55% and 8.68%, respectively. Compared with the mean relative growth rate of CK, treatments of B, C, A, E and D increased by 6.46%, 4.51%, 3.36%, 2.53% and 2.47%, respectively; whereas treatment F decreased by 0.67%. Compared with the average growth rate of cotton aboveground biomass of CK, treatments of B, C, A, D and E increased by 29.69%, 19.20%, 17.94%, 12.38% and 11.67%, respectively; while treatment F decreased by 2.28%. Different topdressing ratios had the greatest effect on cotton stem weight and reproductive organ weight, but had the least effect on boll weight and bud weight ratio. In addition, path analysis showed that the single boll weight and total boll number played an important role in increasing cotton yield. Principal component analysis showed that the nutrient distribution ratio of treatment A ranked the highest, followed by treatment E, and treatment CK was the lowest. The research can provide a technical support for the reasonable topdressing of cotton under salt stress.